1. Field of the Invention
This invention concerns internal combustion engines, and more particularly internal combustion engines having cyclical episodes of combustion in a combustion chamber. Typical of these is the very well known reciprocating piston engine in which a crank mounted piston reciprocates in a cylinder, the end face of the piston together with internal surfaces of the cylinder and its head defining a combustion chamber. However, conventional combustion technology has generally not enabled any significant control over the combustion event in such reciprocating piston internal combustion engines.
2. Description of the Prior Art
In a spark-ignited version of such an engine, a fuel-air charge is formed in the combustion chamber during each cycle, and is ignited and burned to create high pressure gases, which in expanding, drive the piston to create mechanical work output. The charge is typically ignited at a specific locale by a spark plug, and combustion propagates through the remainder of the charge at a rate governed primarily by the air-fuel ratio and by the temperature and pressure of the charge when combustion is initiated.
It is well known that the air-fuel ratio, as well as the temperature and pressure of the charge, must be held to within rather narrow ranges, or the performance of the engine will deteriorate. Consequently, it is known that the beginning, ending, and intensity of combustion can not be controlled in such engines. It is also known that combustion is typically initiated with the spark plug well before the reciprocating piston has fully compressed the fuel-air charge, reflecting the fact that combustion propagates more slowly than desired. Specifically, if combustion is initiated of a time significantly after the piston has fully compressed the fuel-air charge, the combustion process would be far from complete at the time opening of the exhaust values occurs.
In diesel cycle engines, fuel is injected into a highly compressed air charge, the air charge heated by compression to a temperature elevated sufficiently to ensure ignition of the fuel upon injection. Ignition lag delays the ignition and combustion of the fuel such that complete control over the combustion event has not been achieved. Again, heat release is usually initiated prior to full compression of the air to allow sufficient time for combustion.
Since the heat release profiles of both spark-ignited and compression-heated engines have heretofore primarily been governed by such factors as flame speed, evaporation rate, etc., it has not been possible to significantly alter the heat release profile in an attempt to improve engine efficiency. Consequently, efforts aimed at seeking the optimum heat release profile for a particular engine have been nil.
It has heretofore been proposed to achieve so called "hypergolic" combustion, particularly of hydrocarbon fuels in an internal combustion engine, such that ignition delay and the time required to complete combustion are both negligible after the fuel is introduced into an oxidizing atmosphere.
For a detailed discussion, see U.S. Pat. No. 4,448,176; SAE paper no. 850089 "Hypergolic Combustion in an Internal Combustion Engine"; and, SAE paper 820356, "The Influence of Initial Fuel Temperature of Ignition Delay"; each of which are incorporated herein by reference.
As also detailed in the aforementioned references, ignition delay is believed to occur due to the need for the fuel molecules to first be dissassociated into radicals in order to combine with oxygen molecules, which themselves must be dissassociated for oxidation to occur. In a typical combustion process, an ignition device such as a spark plug causes a localized increased concentration of fuel and oxygen radicals in a fuel-air mixture, sufficient for initiation of combustion. The release of heat from that localized combustion in turn causes additional dissassociation of adjacent fuel and oxygen molecules to enable combustion to propagate through the entire charge of fuel-air mixture.
As discussed in the aforementioned U.S. Pat. No. 4,448,176, if there is a pretreatment of the fuel such as to cause a dissassociation of a critical proportion of molecules in each quantity of fuel, much higher than the proportion occurring at ambient temperatures, there is an "activation" of the fuel yielding substantially instantaneous ignition and combustion.
In order that such an increased, critical proportion of fuel molecules be dissassociated into radicals, energy must be expended to bring this proportion of the fuel molecules to the relatively high energy state corresponding to the dissassociated condition of the fuel molecules.
As described in the aforementioned U.S. Pat. No. 4,448,176, if fuel is heated to relatively elevated temperatures in excess of 1000.degree. F., this causes such critical proportion of fuel molecules to be dissassociated to form radicals, since such proportion of the fuel molecules is thereby brought to a high energy state.
In co-pending application Ser. No. 812,863 filed on Dec. 26, 1985, there is described a method and system for heating of the fuel to such elevated temperatures by a regenerative heat exchange process, in which the fuel is circulated through a vessel disposed directly in the combustion chamber, with the combustion chamber insulated to retain heat therein. This arrangement, when combined with preheating of the fuel, as with a heat exchanger in the engine exhaust system, is able to heat the fuel to such sufficiently elevated temperatures, that upon injection into the combustion chamber hypergolic combustion will result.
Alternatively, catalysis is utilized to augment the effect of heating to achieve fuel activation.
A disadvantage of regeneratively heating the fuel is the tendency for cracking of the fuel molecules at high temperatures, and the resultant formation of coke, tending to clog the fuel flow passages. It has been discovered that if the fuel is sustained at the elevated temperatures for only very short time periods, this will avoid this problem.
Also, while such aforementioned regenerative heating method and system will efficiently heat the fuel to such elevated temperatures, a relatively complex fuel circulation system is necessitated and the tendency for coke formation is higher due to the longer times required to achieve heating by heat exchange with the products of combustion produced in prior combustion cycles.
In co-pending application Ser. No. 813,888 filed on Dec. 26, 1985, now U.S. Pat. No. 4,644,925, a method of compressive heating of vaporized fuel is disclosed to achieve activated fuel enabling hypergolic combustion, in which catalysis is alternatively utilized to augment the effect achieved by compression heating alone.
Another method of pretreatment of fuel is disclosed in Ser. No. 446,796, filed on Dec. 3, 1982, now U.S. Pat. No. 4,582,475, in which a corona discharge is utilized to activate fuel passed therethrough prior to combustion, to achieve activation of the fuel molecules by the formation of radicals.
There has also been disclosed in co-pending application Ser. No. 813,892 filed on Dec. 26, 1985, a method of activating fuel by irradiation with ultraviolet radiation to achieve the level of activation of the fuel enabling hypergolic combustion.
In SAE paper 800264 entitled "Gasification of Diesel Fuel for a Low Emission, High Efficiency Engine System"; in Siemens Forsch.-u. Entwickl.-Ber.Bd.6 (1977) Nr. 5, entitled "Autothermal Gasification of Liquid Hydrocarbons by Partial Oxidation"; and Siemens Forsch.-u. Entwickl.-Ber.Bd.7 (1978) Nr.2 entitled "Compact Gas Generator for Fuel Gasification Aboard Motor Vehicles," each of which are hereby incorporated by reference, there is disclosed a method of gasifying liquid hydrocarbon fuels.
In co-pending application Ser. No. 813,882 filed on Dec. 26, 1985, now U.S. Pat. No. 4,651,703, there is disclosed a method and apparatus for activating fuel using such partial catalytic combustion.
Such hypergolic combustion raises the possibility of achieving control over the combustion process such as to precisely control the rate and timing of heat release during a combustion cycle.
It is an object of the present invention to control the combustion event in an internal combustion engine so as to achieve maximized net work ouput from an internal combustion engine, utilizing activated fuel capable of being hypergolically combusted when introduced into a combustion chamber at a rate and over a timed interval predetermined to produce the maximized net work output from the engine.